Getting started with OSGi declarative services - Dirk Fauth

Automotive Service Solutions | AA-AS/EIS2-EU | 27.10.2016
© Robert Bosch GmbH 2016. Alle Rechte vorbehalten, auch bzgl. jeder Verfügung, Verwertung, Reproduktion, Bearbeitung, Weitergabe sowie für den Fall von Schutzrechtsanmeldungen.
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Getting Started with OSGi Declarative Services
Speaker
Dirk Fauth
Software-Architect Rich Client Systeme
Eclipse Committer
Robert Bosch GmbH
Franz-Oechsle-Straße 4
73207 Plochingen
dirk.fauth@de.bosch.com
www.bosch.com
blog.vogella.com/author/fipro/
Twitter: fipro78

OSGi Declarative Services
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 Bundles register (publish) services
 Bundles get (bind) services
 Bundles listen (find) services
Publish-Find-Bind
A BS
register
(publish)
get
(bind)
listen
(find)
<<bundle>> <<bundle>><<service>>

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 (Service) Component
‒ Java class contained in a bundle
‒ Declared via Component Description
 Component Description
‒ XML document to declare a Service Component
 Component Configuration
‒ Component Description that is parameterized with component properties
‒ Tracks the component dependencies and manages the component instance
 Component Instance
‒ Instance of the component implementation class
‒ Created when a Component Configuration is activated
‒ Discarded when the Component Configuration is deactivated
Components

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References
 References
‒ The definition of dependencies to other services.
 Target Services
‒ The services that match the reference interface and target property filter.
 Bound Services
‒ The services that are bound to a Component Configuration.
 Access Strategies
‒ Event Strategy
‒ Lookup Strategy
‒ Field Strategy (1.3)

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Component Types
 Delayed Component
‒ Activated when the service is requested
‒ Needs to specify a service
 Immediate Component
‒ Activated as soon as all dependencies are satisfied
‒ Does not need to specify a service
 Factory Component
‒ Creates and activates Component Configurations

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Component Lifecycle – Immediate
UNSATISFIED
activate ACTIVE
deactivate
Bundle
started
Bundle
stopped
disable
load
enabled
becomes
satisfied
becomes
unsatisfied
if dynamic:
rebinding

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Component Lifecycle – Delayed
UNSATISFIED
activate ACTIVE
deactivate
Bundle
started
Bundle
stopped
disable
load
enabled
becomes
satisfied
becomes
unsatisfied
if dynamic:
rebinding
REGISTERED
get service
becomes
unsatisfied
unget
service

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 Activation consists of the following steps:
1. Load the component implementation class
2. Create the component instance and component context
3. Bind the target services
4. Call the activate method if present
 For Delayed Components the load time is moved to the first request
(including reference bindings)
(see Declarative Services Specification Version 1.3 – 112.5.6 Activation)
Component Lifecycle – Activation

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Component Lifecycle – Factory
UNSATISFIED
activate
ACTIVE
deactivate
Bundle
started
Bundle
stopped
disable
load
enabled
becomes
satisfied
becomes
unsatisfied
if dynamic:
rebinding
FACTORY
newInstance
becomes
unsatisfieddispose
register
unregister

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 Create a bundle for the service API (e.g. org.fipro.inverter.api)
 Create the service interface
Service API
public interface StringInverter {
String invert(String input);
}
 Make the service implementation exchangeable
 Clean dependency hierarchy

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Service API
ErrorHandler
ErrorHandlerImpl
<<consumer bundle>>
<<ErrorHandler Bundle>>
<<SWT>>
<<API>> <<Provider>>

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Metadata
• Create/Modify .bnd file
• Describe OSGi meta-data
• MANIFEST.MF is generated

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 Create a bundle for the service implementation
(e.g. org.fipro.inverter.provider)
 Create the service implementation
Service Provider
@Component
public class StringInverterImpl implements StringInverter {
@Override
public String invert(String input) {
return new StringBuilder(input).reverse().toString();
}
}
@Component
public class StringInverterImpl implements StringInverter {
@Override
public String invert(String input) {
return new StringBuilder(input).reverse().toString();
}
}

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Metadata
• Add API bundle to the Build Path
• Select the annotations to be used

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 Annotation to mark a Java class as a Service Component
 Generates
‒ Component Description XML file
‒ Additional header in MANIFEST.MF
‒ Service-Component header
‒ Provide-Capability header for osgi.service
‒ Require-Capability header for osgi.extender (DS 1.3)
@Component

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 Capability = non-code dependency
 osgi.extender=osgi.component
‒ added to spec with DS 1.3
‒ Equinox DS adapted for DS 1.2 with Eclipse Neon
 osgi.service
‒ specify the provided service implementations
Capabilities
Require-Capability: osgi.extender;
filter:="(&(osgi.extender=osgi.component)(version>=1.3)(!(version>=2.0)))"
Provide-Capability: osgi.service;
objectClass:List<String>="org.fipro.inverter.StringInverter"

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@Component
Type Element Default Type Element Default
configurationPid full qualified class name of
the component
property empty
configurationPolicy optional service full qualified class names of all
directly implemented interfaces
enabled true servicefactory
(depr. in 1.3)
false
factory empty String xmlns lowest DS XML namespace that
supports used features
immediate false if factory or service
true otherwise
name full qualified class name of
the component
reference
(since 1.3)
empty
properties empty scope
(since 1.3)
SINGLETON

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 Component life cycle methods
 Method parameters
‒ ComponentContext
‒ BundleContext
‒ Map<String, ?>
Map containing component properties
‒ int / Integer for (@Deactivate)
‒ <Component Property Type> (DS 1.3)
Type safe access to component properties
@Activate / @Modified / @Deactivate
@Activate
private void activate(
ComponentContext c,
BundleContext b,
Map<String, ?> properties) {
//do some initialization stuff
}

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 Create a bundle for the service consumer
(e.g. org.fipro.inverter.command)
 Create the service consumer implementation
Service Consumer
@Component(property= {"osgi.command.scope:String=fipro",
"osgi.command.function:String=invert"},
service=StringInverterCommand.class
)
public class StringInverterCommand {
private StringInverter inverter;
@Reference
void bindStringInverter(StringInverter inverter) { this.inverter = inverter; }
public void invert(String input) { System.out.println(inverter.invert(input)); }
}
@Component(property= {"osgi.command.scope:String=fipro",
"osgi.command.function:String=invert"},
service=StringInverterCommand.class
)
@Reference
}

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 Specify dependency on other services
 Resolving references is required to satisfy a component
(if the reference is not optional)
 Different strategies for accessing services
‒ Event Strategy
‒ Field Strategy (DS 1.3)
‒ Lookup Strategy
@Reference

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@Reference
 Event Strategy – using event methods for bind/updated/unbind
@Component(...)
@Reference
void updatedStringInverter(
StringInverter inverter, Map<String, ?> properties) { //do something }
void unbindStringInverter(StringInverter inverter) { this.inverter = null; }
}
@Component(...)
@Reference
void updatedStringInverter(
StringInverter inverter, Map<String, ?> properties) { //do something }
void unbindStringInverter(StringInverter inverter) { this.inverter = null; }
}

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 ServiceReference
 <service type>
 <service type> + Map<String, ?>
With DS 1.3
 ComponentServiceObjects
 Different variations of the parameter list
@Reference - Event Method Parameter

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@Reference
 Field Strategy (DS 1.3) – using instance fields
@Component(...)
@Reference
public void invert(String input) {
System.out.println(inverter.invert(input));
}
}
@Component(...)
@Reference
System.out.println(inverter.invert(input));
}
}

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@Reference
 Lookup Strategy (DS 1.2) – lookup everytime needed, do not store
@Component(...)
private ComponentContext context;
private ServiceReference<StringInverter> reference;
@Activate
void activate(ComponentContext context) { this.context = context; }
@Reference
void setStringInverter(ServiceReference<StringInverter> reference) { this.reference = reference; }
StringInverter inverter =
(StringInverter) context.locateService("StringInverter", reference);
...
}
}
@Component(...)
private ServiceReference<StringInverter> reference;
@Activate
@Reference
void setStringInverter(ServiceReference<StringInverter> reference) { this.reference = reference; }
StringInverter inverter =
(StringInverter) context.locateService("StringInverter", reference);
...
}
}

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@Reference
 Lookup Strategy (DS 1.3) – lookup everytime needed, do not store
@Component(...
reference=@Reference(name="inverter", service=StringInverter.class)
)
@Activate
StringInverter inverter = (StringInverter) context.locateService("inverter");
...
}
}
@Component(...
reference=@Reference(name="inverter", service=StringInverter.class)
)
@Activate
StringInverter inverter = (StringInverter) context.locateService("inverter");
...
}
}

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@Reference
Type Element Default Type Element Default
cardinality • 1:1 for event methods
• 1:1 for non-collection
fields, 0..n for collections
unbind unbind<name>
unset<name>
remove<name>
name • bind event method name
without bind prefix
• name of the field
updated updated<name>
if such a method exists
policy STATIC
policyOption RELUCTANT bind
(since 1.3)
the name of the annotated
method or empty
service full qualified class name of
the referenced service
field
(since 1.3)
the name of the annotated field
or empty
target empty String fieldOption
(since 1.3)
REPLACE
scope
(since 1.3)
BUNDLE

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Further information
 OSGi Compendium Specification
https://www.osgi.org/developer/specifications/
 enRoute Documentation
http://enroute.osgi.org/book/210-doc.html
 Blog posts
Getting Started with OSGi Declarative Services
http://blog.vogella.com/2016/06/21/getting-started-with-osgi-declarative-services/
OSGi Component Testing
http://blog.vogella.com/2016/07/04/osgi-component-testing/
Configuring OSGi Declarative Services
http://blog.vogella.com/2016/09/26/configuring-osgi-declarative-services/

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